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Side by Side Diff: third_party/google/protobuf/reflection.py

Issue 1162993005: Renamed google.protobuf to protobuf26 (Closed) Base URL: svn://svn.chromium.org/chrome/trunk/tools/depot_tools
Patch Set: Addressed comments Created 5 years, 6 months ago
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1 # Protocol Buffers - Google's data interchange format
2 # Copyright 2008 Google Inc. All rights reserved.
3 # http://code.google.com/p/protobuf/
4 #
5 # Redistribution and use in source and binary forms, with or without
6 # modification, are permitted provided that the following conditions are
7 # met:
8 #
9 # * Redistributions of source code must retain the above copyright
10 # notice, this list of conditions and the following disclaimer.
11 # * Redistributions in binary form must reproduce the above
12 # copyright notice, this list of conditions and the following disclaimer
13 # in the documentation and/or other materials provided with the
14 # distribution.
15 # * Neither the name of Google Inc. nor the names of its
16 # contributors may be used to endorse or promote products derived from
17 # this software without specific prior written permission.
18 #
19 # THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
20 # "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
21 # LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
22 # A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
23 # OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
24 # SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
25 # LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
26 # DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
27 # THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
28 # (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
29 # OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
30
31 # This code is meant to work on Python 2.4 and above only.
32
33 """Contains a metaclass and helper functions used to create
34 protocol message classes from Descriptor objects at runtime.
35
36 Recall that a metaclass is the "type" of a class.
37 (A class is to a metaclass what an instance is to a class.)
38
39 In this case, we use the GeneratedProtocolMessageType metaclass
40 to inject all the useful functionality into the classes
41 output by the protocol compiler at compile-time.
42
43 The upshot of all this is that the real implementation
44 details for ALL pure-Python protocol buffers are *here in
45 this file*.
46 """
47
48 __author__ = 'robinson@google.com (Will Robinson)'
49
50
51 from google.protobuf.internal import api_implementation
52 from google.protobuf import descriptor as descriptor_mod
53 from google.protobuf import message
54
55 _FieldDescriptor = descriptor_mod.FieldDescriptor
56
57
58 if api_implementation.Type() == 'cpp':
59 if api_implementation.Version() == 2:
60 from google.protobuf.pyext import cpp_message
61 _NewMessage = cpp_message.NewMessage
62 _InitMessage = cpp_message.InitMessage
63 else:
64 from google.protobuf.internal import cpp_message
65 _NewMessage = cpp_message.NewMessage
66 _InitMessage = cpp_message.InitMessage
67 else:
68 from google.protobuf.internal import python_message
69 _NewMessage = python_message.NewMessage
70 _InitMessage = python_message.InitMessage
71
72
73 class GeneratedProtocolMessageType(type):
74
75 """Metaclass for protocol message classes created at runtime from Descriptors.
76
77 We add implementations for all methods described in the Message class. We
78 also create properties to allow getting/setting all fields in the protocol
79 message. Finally, we create slots to prevent users from accidentally
80 "setting" nonexistent fields in the protocol message, which then wouldn't get
81 serialized / deserialized properly.
82
83 The protocol compiler currently uses this metaclass to create protocol
84 message classes at runtime. Clients can also manually create their own
85 classes at runtime, as in this example:
86
87 mydescriptor = Descriptor(.....)
88 class MyProtoClass(Message):
89 __metaclass__ = GeneratedProtocolMessageType
90 DESCRIPTOR = mydescriptor
91 myproto_instance = MyProtoClass()
92 myproto.foo_field = 23
93 ...
94
95 The above example will not work for nested types. If you wish to include them,
96 use reflection.MakeClass() instead of manually instantiating the class in
97 order to create the appropriate class structure.
98 """
99
100 # Must be consistent with the protocol-compiler code in
101 # proto2/compiler/internal/generator.*.
102 _DESCRIPTOR_KEY = 'DESCRIPTOR'
103
104 def __new__(cls, name, bases, dictionary):
105 """Custom allocation for runtime-generated class types.
106
107 We override __new__ because this is apparently the only place
108 where we can meaningfully set __slots__ on the class we're creating(?).
109 (The interplay between metaclasses and slots is not very well-documented).
110
111 Args:
112 name: Name of the class (ignored, but required by the
113 metaclass protocol).
114 bases: Base classes of the class we're constructing.
115 (Should be message.Message). We ignore this field, but
116 it's required by the metaclass protocol
117 dictionary: The class dictionary of the class we're
118 constructing. dictionary[_DESCRIPTOR_KEY] must contain
119 a Descriptor object describing this protocol message
120 type.
121
122 Returns:
123 Newly-allocated class.
124 """
125 descriptor = dictionary[GeneratedProtocolMessageType._DESCRIPTOR_KEY]
126 bases = _NewMessage(bases, descriptor, dictionary)
127 superclass = super(GeneratedProtocolMessageType, cls)
128
129 new_class = superclass.__new__(cls, name, bases, dictionary)
130 setattr(descriptor, '_concrete_class', new_class)
131 return new_class
132
133 def __init__(cls, name, bases, dictionary):
134 """Here we perform the majority of our work on the class.
135 We add enum getters, an __init__ method, implementations
136 of all Message methods, and properties for all fields
137 in the protocol type.
138
139 Args:
140 name: Name of the class (ignored, but required by the
141 metaclass protocol).
142 bases: Base classes of the class we're constructing.
143 (Should be message.Message). We ignore this field, but
144 it's required by the metaclass protocol
145 dictionary: The class dictionary of the class we're
146 constructing. dictionary[_DESCRIPTOR_KEY] must contain
147 a Descriptor object describing this protocol message
148 type.
149 """
150 descriptor = dictionary[GeneratedProtocolMessageType._DESCRIPTOR_KEY]
151 _InitMessage(descriptor, cls)
152 superclass = super(GeneratedProtocolMessageType, cls)
153 superclass.__init__(name, bases, dictionary)
154
155
156 def ParseMessage(descriptor, byte_str):
157 """Generate a new Message instance from this Descriptor and a byte string.
158
159 Args:
160 descriptor: Protobuf Descriptor object
161 byte_str: Serialized protocol buffer byte string
162
163 Returns:
164 Newly created protobuf Message object.
165 """
166 result_class = MakeClass(descriptor)
167 new_msg = result_class()
168 new_msg.ParseFromString(byte_str)
169 return new_msg
170
171
172 def MakeClass(descriptor):
173 """Construct a class object for a protobuf described by descriptor.
174
175 Composite descriptors are handled by defining the new class as a member of the
176 parent class, recursing as deep as necessary.
177 This is the dynamic equivalent to:
178
179 class Parent(message.Message):
180 __metaclass__ = GeneratedProtocolMessageType
181 DESCRIPTOR = descriptor
182 class Child(message.Message):
183 __metaclass__ = GeneratedProtocolMessageType
184 DESCRIPTOR = descriptor.nested_types[0]
185
186 Sample usage:
187 file_descriptor = descriptor_pb2.FileDescriptorProto()
188 file_descriptor.ParseFromString(proto2_string)
189 msg_descriptor = descriptor.MakeDescriptor(file_descriptor.message_type[0])
190 msg_class = reflection.MakeClass(msg_descriptor)
191 msg = msg_class()
192
193 Args:
194 descriptor: A descriptor.Descriptor object describing the protobuf.
195 Returns:
196 The Message class object described by the descriptor.
197 """
198 attributes = {}
199 for name, nested_type in descriptor.nested_types_by_name.items():
200 attributes[name] = MakeClass(nested_type)
201
202 attributes[GeneratedProtocolMessageType._DESCRIPTOR_KEY] = descriptor
203
204 return GeneratedProtocolMessageType(str(descriptor.name), (message.Message,),
205 attributes)
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